Water shoots up at end of flush

[SV Aquavit]

When the bowl is almost empty, water shoots up into the toilet.

Here's a video

splashing.mp4

BTW, it's not pee or poop. It's some old head lube I had. Makes it easier to see what's happening.

Does this look like a joker valve issue? Something else?

The head is a Wilcox Crittenden Skipper I recently rebuilt with a kit the PO had purchased when they were still available.

[siamese]

Okay...it might as well be me:

It's a bidet!

[Bill O]

Originally Posted by siamese

It's a bidet!

[Bowdrie]

There is a "flap valve", it has a bronze piece riveted to the rubber part.
Underneath that valve is a "hairpin spring".
The spring fits into a "U" shaped holder, and the holder fits in holes which are covered by the stationary section of the valve whilst the "spring" part of the hairpin spring pushes up
against the bronze part and holds the flap valve against the big rubber gasket above it.
If there is insufficient water in the piston bore to affect a hydraulic seal on the pump stroke the spring is supposed to create the seal.
The springs are quite long-lived, but one should have been in the service kit.
It's also common when someone services the unit to forget to install that spring.
This is the holder for the spring.
https://marinesan.com/pin-for-flap-v...g-aftermarket/
Here is a parts breakdown of the unit.
The holder for the spring is #54, and the spring itself is #55, the flap valve is #56.
I don't know if aftermarket springs are available.
https://marinesan.com/packing-material-1ft-aftermarket/